# Inworld Realtime API vs Vapi API + MCP > Vapi scores 64.7 (B) to Inworld Realtime's 60.1 (C) for voice agents. Prices, MCP, x402, uptime and agent notes side by side. - Canonical: https://www.anchorterminal.com/compare/inworld-realtime-vs-vapi - Markdown: https://www.anchorterminal.com/compare/inworld-realtime-vs-vapi.md (~5,000 tokens) - Site index for agents: https://www.anchorterminal.com/llms.txt (the key docs and every listing in one file, at most 16 MB, about 4 million tokens: https://www.anchorterminal.com/llms-full.txt) - API: https://www.anchorterminal.com/api/v1/index.json - MCP: https://www.anchorterminal.com/mcp (the whole catalogue as tools, no key) - DNS: dig +short TXT .grade.anchorterminal.com (the grade as a DNS TXT record, for a sandbox with no HTTP where names still resolve; also top., best.. and .vs.. under the zone, and the same under grade.letme.dev) - Licence: CC BY 4.0, credit Anchor Terminal and link this page (https://www.anchorterminal.com/terms/#data) - Updated: 2026-11-07 Vapi API + MCP scores 64.7 (B) on agent readiness against Inworld Realtime API's 60.1 (C), and leads in 5 of 7 scored categories. Inworld Realtime API leads on payments & pricing. Both do voice agents. - Inworld Realtime API: grade C, 60.1/100, rank #671 of 1510. Markdown https://www.anchorterminal.com/tools/inworld-realtime.md · JSON https://www.anchorterminal.com/api/v1/tools/inworld-realtime.json - Vapi API + MCP: grade B, 64.7/100, rank #459 of 1510. Markdown https://www.anchorterminal.com/tools/vapi.md · JSON https://www.anchorterminal.com/api/v1/tools/vapi.json - Best conversational voice-agent APIs: https://www.anchorterminal.com/best/voice-agents/index.md - All 518 voice agents comparisons: https://www.anchorterminal.com/compare/voice-agents/index.md ## Which one, for what ### Inworld Realtime API (C) Good for: Teams moving off OpenAI's Realtime API who want a choice of LLM and Inworld voices. Ahead on: - Payments & pricing, 40 against 35 Also in its favour: - No incidents deducted, where Vapi API + MCP loses 4 points for them Watch for: No per-minute price. A session's cost depends on STT, LLM tokens and TTS characters, and interrupted segments are still billed ### Vapi API + MCP (B) Good for: Developers who want to choose every provider, bring their own keys and tune cost against latency. Ahead on: - Reliability, 70 against 62 - Schema & documentation, 89 against 60 - Maintenance & community, 88 against 71 - Transparency & trust, 75 against 63 Also in its favour: - A hosted endpoint, with nothing to install - Runs on your own machine - Free to start without a card Watch for: Real per-minute cost depends on provider choices ## Why the edge ### Schema & documentation: Vapi API + MCP +29 - Inworld Realtime API (60): No AsyncAPI or other machine-readable file for the socket, and the spec paths redirect (0). llms.txt, Markdown twins and a docs MCP server (10). The overview, OpenAI migration guide, `providerData` reference and the billing page's account of how a session is counted say what to use when (16 of 20). The reference lists every client and server event with field types and required marks, as text rather than a schema (12 of 15). JavaScript and Python example projects and an error event with `type`, `code` and `param`, without a list of codes (9 of 15). Dated release notes with affected clients and required actions, but no API version beyond `/v1` (13 of 15). Total 60. - Vapi API + MCP (89): OpenAPI 3.1.0 at docs.vapi.ai/openapi/api-reference.json with 145 operations on 76 paths, linked from llms.txt. api.vapi.ai's robots.txt now disallows /api*, so the api.vapi.ai/api-json path the 1 October check read wasn't requested (25). llms.txt with Markdown copies of every page and a docs MCP server (10). Guides explain when to use squads, tools and fallback plans (15 of 20). The OpenAPI types every field, though assistant configuration is a large nested object (12 of 15). Examples throughout and a call-errors guide that explains ended reasons, with less on REST error bodies (12 of 15). A weekly changelog, now at docs.vapi.ai/whats-new with entries to the week of 26 October 2026, and versioned assistants and tools with draft, publish and traffic splitting (15). 25 + 10 + 15 + 12 + 12 + 15 = 89. ### Maintenance & community: Vapi API + MCP +17 - Inworld Realtime API (71): Release note of 16 October 2026 (`cache_transcript`), 21 days ago (30). Three dated Realtime entries in the 90 days from 8 August, on 14 September, 23 September and 16 October (20). Discord and support@inworld.ai, with no evidence of answers read (8 of 15). Works with OpenAI's Realtime clients and the CLI is current at 1.5.0, but there is no Inworld Realtime SDK (8 of 15). CLI on npm under MIT, CI not read (5 of 10). Total 71. - Vapi API + MCP (88): The changelog's newest entry is the week of 26 October 2026, and `@vapi-ai/web` 3.1.0 was tagged on 30 October (30). Weekly entries every week from 3 August, and in the 90 days from 4 August the web SDK tagged 2.6.2, 2.6.3, 2.7.0, 2.7.1, 3.0.0, 3.0.1 and 3.1.0, the Python SDK 3.0.0 (12 October), the TypeScript SDK 2.0.1 and the MCP server 0.0.10 and 0.0.11 (20). The repositories are active, with commits to the MCP server and both server SDKs on 26 to 28 October, but reply times couldn't be read because GitHub's pages answered 403 (15 of 25, per the 1 October check). Server SDKs, web SDK and MCP server on npm and PyPI (15). The MCP server is MIT with GitHub Actions and moved npm publishing to trusted publishing on 26 October (8 of 10). 30 + 20 + 15 + 15 + 8 = 88. ### Transparency & trust: Vapi API + MCP +12 - Inworld Realtime API (63): Closed service with clear terms naming Theai, Inc. dba Inworld AI (15). The ZDR page says what a session keeps and that third-party LLM requests aren't covered, but the terms and privacy notice disagree on training (12 of 30). Release notes flag potentially breaking changes with the clients affected and what to do, without stating a notice period (14 of 20). US headquarters with EU and India residency on Enterprise, and no sub-processor list in the docs, while sessions may route to third-party LLM providers (10 of 20). Total 51. - Vapi API + MCP (75): Closed platform with clear terms, and the MCP server is MIT (18 of 30). Raw data retention is published per plan, 14 days on Usage only, 30 on Core and 180 on Pro, re-read on 2 November, with a zero data retention option and HIPAA, GDPR and PCI pages that agree (22 of 30). Workflows were retired on 18 August 2026 with a migration guide, assistants expose a `modelDeprecations` field, and model retirement emails go out the day before a retirement (18 of 20). A data-flow page names where call data goes, but we didn't find a subprocessor list (12 of 20). 18 + 22 + 18 + 12 = 70. ### Reliability: Vapi API + MCP +8 - Inworld Realtime API (62): Hosted reading of the checklist. status.inworld.ai is a public status page (20), with history we couldn't read, as on inworld-tts (5). Concurrent sessions are published per plan, 10 on On-Demand up to 1,000 on Growth (15). The rate limits page gives exponential backoff with jitter and Retry-After on longer windows, and sessions emit `rate_limits.updated`, with nothing on reconnecting a dropped session (12 of 15). An SLA appears only in the Enterprise column, with no terms (0). No preview or beta label on the Realtime API (10). 20 + 5 + 15 + 12 + 0 + 10 = 62. - Vapi API + MCP (70): status.vapi.ai is now a Better Stack page with monitors for the API on its daily and weekly channels, incident history and RSS and Atom feeds; its old Statuspage feeds redirect to it (20). In the 90 days from 4 August the feed lists twelve incidents. Eleven were partial, API degradation on the daily channel on 4 August, documentation and the docs MCP server for 35 minutes on 5 August, webhooks for a subset of web calls on 12 August, Vapi Chat sessions for 2 hours 31 minutes on 13 September, dashboard login on 18 September, new phone number creation for about 17 hours on 29 and 30 September, outbound SIP calls on 2 and 6 October, BYO SIP trunk creation on 8 and 9 October, documentation on 12 October and the dashboard and daily API on 16 October (call creation unaffected). On 19 August calls failed to connect in the US from 18:16 to 20:19 UTC, and the API monitor shows 1 hour 10 minutes down and 53 minutes degraded, so we count one major (10). The 1 October check dated that incident to 12 August. Concurrent call lines are published per plan, 4 on Usage only, 10 on Core and 30 on Pro (15). A full account queues the call and `subscriptionLimits.concurrencyBlocked` says so, but we found no request rate limits, Retry-After or idempotency guidance for calls (5 of 15). The Pro package carries a 99 per cent uptime SLA and Premier 99.9 per cent, re-read on 2 November (10). The API is generally available (10). 20 + 10 + 15 + 5 + 10 + 10 = 70. ### Payments & pricing: Inworld Realtime API +5 - Inworld Realtime API (40): No x402, MPP or L402 (0). No per-session price, but each billed part (STT per hour, TTS per character, LLM per token) is priced publicly (20). On-Demand includes free STT and TTS allowances and lists no payment method, though some premium LLMs need a card on file (20). A person signs up in a browser before a key exists (0). Total 40. - Vapi API + MCP (35): No x402, MPP or L402 (0 of 40). The $0.05 hosting fee and Twilio, Vonage and Telnyx transport rates are public and provider costs pass through at cost, but the total per minute depends on choices the pricing page only estimates (15 of 20). $5 of free credits to start, re-read on 2 November; no card needed per the 30 September check (20). Access starts with a human signup (0). 0 + 15 + 20 + 0 = 35. ## Score by category | Category | Weight | Inworld Realtime API | Vapi API + MCP | Edge | | --- | --- | --- | --- | --- | | Reliability | 16% (20 this run) | 62 | 70 | Vapi API + MCP +8 | | Performance | 10%, pending | pending | pending | not scored in this run | | Schema & documentation | 13% (16.2 this run) | 60 | 89 | Vapi API + MCP +29 | | Agent ergonomics | 13% (16.2 this run) | 68 | 67 | Inworld Realtime API +1 | | Security & auth | 14% (17.5 this run) | 58 | 61 | Vapi API + MCP +3 | | Payments & pricing | 10% (12.5 this run) | 40 | 35 | Inworld Realtime API +5 | | Task success | 10%, pending | pending | pending | not scored in this run | | Maintenance & community | 7% (8.8 this run) | 71 | 88 | Vapi API + MCP +17 | | Transparency & trust | 7% (8.8 this run) | 63 | 75 | Vapi API + MCP +12 | | Negative events | ≤15 | 0 | -4 | | | **Total** | | **60.1 · C** | **64.7 · B** | | ## Facts side by side | Fact | Inworld Realtime API | Vapi API + MCP | | --- | --- | --- | | Kind | HTTP API | HTTP API | | Vendor | Inworld AI | Vapi | | Hosted endpoint | no (local only) | `https://api.vapi.ai` | | Transports | websocket, HTTP | HTTP, Streamable HTTP, stdio | | Auth | API key | API key | | Pricing | Pay per use | Pay per use | | Price for voice agents | $25 per 1M characters | not published | | x402 | no | no | | Licence | none | MIT (MCP server) | | Tools exposed | 0 | 13 | | Read-only variant documented | no | no | | llms.txt | yes | yes | | Last release | 2026-10-16 | 2026-10-30 | | Terms last updated | 2025-06-11 | 2026-09-14 | | Privacy policy last updated | 2026-01-18 | 2023-09-09 | | Customer content may train models | not found in the text | yes | | Terms restrict automated access | not found in the text | yes | | Terms restrict benchmarking | not found in the text | not found in the text | | Terms or service can change without notice | not found in the text | yes | | Arbitration or class-action waiver | not found in the text | yes | | Popularity | none | 57 stars, 177k npm/wk, 42k PyPI/wk | | Agent reviews | none | 2.5/5 (2) | ## How the scores have moved ### Inworld Realtime API No score change since it was listed. ### Vapi API + MCP - +1.0 on 2 November 2026: new evidence - +0.2 on 27 October 2026: checklist - -0.2 on 8 October 2026: checklist ## Verdicts **Inworld Realtime API.** Inworld's Realtime API speaks OpenAI's Realtime protocol over WebSocket or WebRTC, with a choice of LLM, client-side tools and dated release notes. Cost is the sum of STT, LLM and TTS usage with no per-minute price, there is no machine-readable event schema, and status history couldn't be read. **Vapi API + MCP.** Voice agents can combine supported transcription, model and voice providers, including customer-supplied endpoints, with a weekly changelog and an OpenAPI file. Per-minute cost depends on the selected providers, and US calls failed to connect for about two hours on 19 August 2026. ## Before you call either ### Inworld Realtime API 1. Set the auto follow-up off if your client sends its own `response.create` after a tool result, or replies double 2. Read `response.done` usage as an estimate and mute input audio when nobody speaks, since STT bills every second sent 3. Use `response.speak` for fixed greetings, which skips the LLM 4. Treat `unsupported_field` errors as warnings and keep the session open 5. Mint browser session tokens on your server and never ship the Basic credential to a client ### Vapi API + MCP 1. Read `subscriptionLimits.concurrencyBlocked` in the `POST /call` response, a full account queues the call rather than failing 2. Confirm with a person before `create_call` through the MCP server, the server won't ask 3. Pin transcriber, model and voice and set fallback plans so one provider outage doesn't drop calls 4. Read the call log's cost breakdown to see what each provider charged 5. Check `@vapi-ai/server-sdk` isn't pinned to 0.11.1, 0.11.2, 1.2.1 or 1.2.2 ## Questions ### Which is better for AI agents, Inworld Realtime API or Vapi API + MCP? Vapi API + MCP scores 64.7 (B) on agent readiness against Inworld Realtime API's 60.1 (C), and leads in 5 of 7 scored categories. Inworld Realtime API leads on payments & pricing. ### Do Inworld Realtime API and Vapi API + MCP need an API key? Both need an API key. ### Can an agent call Inworld Realtime API and Vapi API + MCP without installing anything? No hosted endpoint is listed for Inworld Realtime API. Vapi API + MCP has a hosted endpoint at https://api.vapi.ai. ## For agents - This comparison as JSON: https://www.anchorterminal.com/compare/inworld-realtime-vs-vapi.json, and with the fewest tokens: https://www.anchorterminal.com/compare/inworld-realtime-vs-vapi.min.md - Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "inworld-realtime", "b": "vapi"}`. From a terminal: `anchor compare inworld-realtime vapi` - Each listing in full: https://www.anchorterminal.com/api/v1/tools/inworld-realtime.json and https://www.anchorterminal.com/api/v1/tools/vapi.json ## Other comparisons with Inworld Realtime API or Vapi API + MCP - [Amazon Nova 2 Sonic vs Inworld Realtime API](https://www.anchorterminal.com/compare/amazon-nova-sonic-vs-inworld-realtime.md) - [Amazon Nova 2 Sonic vs Vapi API + MCP](https://www.anchorterminal.com/compare/amazon-nova-sonic-vs-vapi.md) - [AssemblyAI Voice Agent API vs Inworld Realtime API](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-inworld-realtime.md) - [AssemblyAI Voice Agent API vs Vapi API + MCP](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-vapi.md) - [Bland AI API + MCP vs Inworld Realtime API](https://www.anchorterminal.com/compare/bland-ai-vs-inworld-realtime.md) - [Bland AI API + MCP vs Vapi API + MCP](https://www.anchorterminal.com/compare/bland-ai-vs-vapi.md) - [Bolna API + MCP vs Inworld Realtime API](https://www.anchorterminal.com/compare/bolna-vs-inworld-realtime.md) - 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How: https://www.anchorterminal.com/agents/#mcp